1. Field of the Invention
This invention relates to methods and apparatus for the transmission and reception of the broadcast signals modulated with encoded data. More particularly this invention relates to methods and apparatus for reception of broadcast signals modulated with encoded data employing receiver diversity and time diversity techniques.
2. Description of Related Art
Diversity techniques are well known in the art to insure the quality of reception in an environment where the broadcast signals are fading. Transmitter diversity employs multiple antennas or multiple transmitters coupled to multiple antennas to broadcast signals such that a receiver is more likely to receive one of the signals.
In receiver diversity, multiple antennas or multiple antennas coupled to multiple receivers are employed to receive the broadcast signal. In the fading channel, the likelihood that one of the receivers will capture the broadcast signal justifies the expense of additional antennas and receivers.
Refer now to FIGS. 1a and 1b for a review of receiver diversity of the prior art. In FIG. 1a, the transmitter 5 modulates a transmit signal such as an RF frequency with a data signal and transfers the modulated transmit signal to a transducer such as the antenna 10. The antenna 10 radiates a broadcast signal that results from the modulated transmit signal. The broadcast signal as is known is a wave front of electromagnetic energy shown here as separate broadcast signals 12, 13, and 14. Geographic obstacles such as mountains and hills 15 and buildings 20 may block or reflect the broadcast signals 12, 13, and 14 such that the amount of energy arriving at any of the antennas 25a, 25b, 25c is not sufficient to be detected by the receiver 35. If there were just one antenna, then any of the broadcast signals 12, 13, and 14 cannot be distinguished by the receiver. However, the multiple antennas 25a, 25b, 25c allow the antenna switch 30 to monitor the strength of the received broadcast signals 12, 13, and 14 and to select one of the antennas 25a, 25b, 25c having the strongest signal for transfer to the receiver 35. This allows the receiver 35 to have the highest quality signal to process to extract the received information.
In FIG. 1b, the transmitter 5 similarly modulates a transmit signal such as an RF frequency with a data signal and transfers the modulated transmit signal to a transducer such as the antenna 10. The antenna 10 radiates a broadcast signal that results from the modulated transmit signal. The broadcast signal, as is known, is a wave front of electromagnetic energy shown here as separate broadcast signals 12, 13, and 14. The geographic obstacles such as the mountains and hills 15 and the buildings 20 similarly may block or reflect the broadcast signals 12, 13, and 14. In this example, the antennas 25a, 25b, 25c are coupled respectively to the receivers 35a, 35b, 35c. Dependent upon the strength of the broadcast signals 12, 13, and 14 any of the antennas 25a, 25b, 25c may not have sufficient for detection by its respective receiver 35a, 35b, 35c. As in the previous example, if only one antenna and receiver existed and it was blocked from receiving the broadcast signals 12, 13, and 14, the receiver would not be able to recover the data signal. All the receivers 35a, 35b, or 35c are connected to the receiver switch 40, which dependent upon the quality of the received and recovered signal switches selects the receiver 35a, 35b, 35c having the best recovered data signal.
The examples of FIGS. 1a and 1b illustrate a wireless radio frequency (RF) application for diversity. Refer now to FIG. 2 for an example of receiver diversity as applied to a wireless infrared application for digital audio headphones. The transmitter 50 is provided digitally encoded audio signals. The transmitter 50 formats the digitally encoded audio signals with synchronization, control, and error signals. The formatted encoded data modulates a transmit signal similar to the RF wireless, except in this case the signal may be pulse positioned modulated rather than frequency shift keyed as in RF wireless. The modulated signal is used to control the radiation of a light signal from the light emitting diode (LED) 55. The light signal 85 is broadcast to the headphones 60. The headphones 60 have at least two photodetectors 70a and 70b. The photodetectors 70a and 70b are generally placed on the outer sides of the headphones 60 to receive the light signal 85. The detected electrical signals of the photodetectors 70a and 70b are transferred to the receiver 75, which demodulates and reformats the encoded audio signals for transfer to the speakers 80a and 80b. The speakers 80a and 80b are placed in close proximity to the ears of the person 65 wearing the headphones 60. If the system had only one photodetector 70a or 70b, the light signal 85 would be not be detectable if the photodetector 70a or 70b was not pointed essentially directly at the LED transmitter 55. Having two photodetectors 70a and 70b allows the receiver to always have detected electrical signals. The photodetectors 70a and 70b maybe selected by a switch that which of the photodetectors 70a or 70b has sufficient signal for detection. Alternately, there, in fact, may be two receivers with a selection circuit determining which receiver transfers the received audio to the speakers 80a and 80b. 
A technique commonly referred to as time diversity employs interleaving of the encoded data and error correction coding to insure that the received digital audio signals are recovered. The interleaving separates contiguous data packets of the digital audio and transfers them at non-contiguous times. This allows for errors to occur within the encoded data and to the encoded data to be recovered when the received digital audio data is rearranged to de-interleave the data packets and then have error detection and correction performed on the received data. Thus even marginally received broadcast signals can be successfully received and the data recovered.
U.S. Pat. No. 6,351,630 (Wood, Jr.) describes a wireless communications system having transponder coupled to one of multiple selectable antennas. A look-up table holds data representing antennas, and having pointers to define an order in which antennas will be used to attempt communication with second transponder
U.S. Pat. No. 6,272,190 (Campana, Jr.) provides a system and method for wireless transmission and receiving of information. The method includes transmitting data and then after a time delay retransmitting the data. The data for each transmission contains an error correction code. Upon receiving the first and second data transmissions, the data is processed to identify, by use of the error correction code, erroneous data within at least one of the data transmissions. The identified erroneous data is replaced with non-erroneous data from the other data transmission.
U.S. Pat. No. 6,185,258 (Alamouti, et al.) teaches a transmitter diversity technique for wireless communications. A simple block coding arrangement is created with symbols transmitted over a plurality of transmit channels. The diversity created by the transmitter utilizes space diversity and either time or frequency diversity.
U.S. Pat. No. 6,181,749 (Urabe, et al.) details a diversity receiver. A demodulator obtains modulated data to a number of channels. The channels have subband filters and differential detectors for demodulating the data. Error estimating circuits estimate and output the numbers of erroneous symbols and error locations for each channel. A data comparator compares the demodulated data corresponding to the error locations with the demodulated data in the corresponding locations in other channels to determine whether the error location is correct. The data comparator provides a decision signal in response to the determination. A data selector selects one of the demodulated data from the channels on the basis of the numbers of erroneous symbols and the decision signals and outputs the data as selected data.
U.S. Pat. No. 6,088,407 (Buternowsky, et al.) describes a digital diversity receiver system employing one or more transmitters, a plurality of receivers, and at least one two-way personal paging unit or pager. The two-way pager receives pages from the transmitter, and sends response signals, which are detected by the receivers. A microdiversity receiver is described as two receiver components provided at a single receiver site, with a separate antenna for each receiver component. Signals as received at the different receivers can be compared and have the accuracy indication information combined to increase the reliability of the system in detecting and decoding the pager response symbols.
U.S. Pat. No. 5,799,042 (Xiao) describes a wireless digital communication systems that apply an antenna diversity scheme to combat fading in a received radio system having a single receiver front-end comprises a simple and robust antenna diversity scheme. Radio signals transmitted to the receiving antennas has redundant information for allowing error correction at reception side.
U.S. Pat. No. 5,073,900 (Mallinckrodt) provides a cellular communications system is provided using spread spectrum system with code division multiple access (CDMA), and employing forward error correction coding (FECC) to enhance the effective gain and selectivity of the system. A digital data interleaving feature reduces fading.
U.S. Pat. No. 4,517,669 (Freeburg, et al.) describes a method and apparatus for coding messages communicated between a primary station and remote stations of a data communications system. The apparatus employs an antenna diversity scheme for a communications controller at the primary station. Variable length messages are communicated between a general communications controller (GCC) and a plurality of portable and mobile radios. The variable length messages include a bit synchronization field, a message synchronization field and a plurality of channel data blocks for efficiently and reliably handling long strings of data or text. Each channel data block includes an information field, a parity field for error-correcting the information field and a channel state field indicating whether or not the radio channel is busy or free.
Japanese Patent Laid-Open No. 4-8031 JP4008031 (Hiroyuki) describes a reception diversity system, which generates an error correcting signal indicating the correction every time received data is corrected. The error correcting signal is sent to an error correcting signal comparator, which counts the error correcting signal compares the signals from multiple receivers to decide which receiver is providing the best quality reception.
Japanese Patent Laid-Open No. 1-265739 (Kiyoyuki, et al.) provides a system for minimizing the effect of reception level fluctuation and phase fluctuation due to fading. The transmitter sends transmission information encoded with error detection and correction codes. The receiver decodes the received information by plural antennas. The system performs an error detection and correction on the received information and based on the amount of errors present in the received information selects the received information from the antenna with least error among the received information sets from each of the antennas.
“Cochannel Interference Suppression Through Time/Space Diversity,” Calderbank, et al., IEEE Transactions on Information Theory, May 2000, Volume: 46, Issue: 3, pp. 922-932 discusses wireless systems that are subject to a time-varying and unknown a priori combination of cochannel interference, fading, and Gaussian noise. The wireless systems discussed provide diversity in time by channel coding.
“Interference Cancellation Using Antenna Diversity for EDGE-Enhanced Data Rates in GSM and TDMA/136,” Bladsjo et al., Proceeding Vehicular Technology Conference, 1999, pp. 1956-1960, vol.4, discusses the evaluation of EDGE (enhanced data rates for global evolution). The paper further discusses antenna diversity, which enables interference-cancellation methods.